Blast furnace cyanide outlet



April 1944- R. FRANCHOTV 2,347,045

BLAST FURNACE CYANIDE OUTLET Filed Jan. 29, 1942 Patented Apr. 18, 1944 2,347,045 I BLAST FURNACE cramps OUTLET Richard Franchot, Washington, D. (3., assignor to Ferro Nitrogen Corporation, Washington,

a corporation of the District of Columbia Application January 29, 1942, Serial No. 428,770

Claims.

This invention relates to a blast furnace cyanide outlet and it comprises means for controlling the accumulation of alkali cyanide in a blast furnace producing pig iron wherein wide horizontal openings in the furnace wall above the bosh are connected through outside vertical con duits running upward to narrow downwardl directed nozzles set in a horizontal plane and serving as throttles and as inlets for cyanide vapor laden gases into cooling and condensing chambers, the cross sectional area of each nozzle being so small in relation to that of the wall opening and connectin conduit that the velocity of gas flow out of the furnace i insufficient to carry substantial amounts of solid materials out of the furnace; and it further comprises a method of controlling the burden ratio in smelting iron ores with coke wherein limited amounts of cyanide vapor are withdrawn through the throttled outlets to lower the concentration thereof in the combustion gases and the burden is increased in proportion to the efiected decrease in said cyanide concentration; all as more fully hereinafter set forth and as claimed.

The presence of alkali cyanides in the hotter zones of the blast furnace making pig iron was first discovered by Bunsen and Playfair about 1840. Since that time charcoal has been almost entirely superseded by coke as the fuel used for smelting iron ore to make pi iron. Lowthian Bell about 1875 found in the coke furnace quantities of potassium cyanide comparable to those discovered by Bunsen in the charcoal furnace. The alkali cyanide found in the blast furnace is of course derived from small amounts of potash and soda in the smelting materials, ore, coke and limestone. Few attempts have been made to extract the cyanide found to be always present in the blast furnace. These attempts have not been successful.

As a matter of fact, the quantities of cyanide found to be present in the hearth and bosh regions are always great in relation to the small quantities of potash contained in the ore, coke and limestone fed to the furnace. These relatively large quantities of cyanide are associated with the accumulation of potash b successive vaporization and condensation, the fumace thus functioning much like a reflux condenser. For example, a furnace having a potash input equivalent to little more than 1 per cent potassium cyanide, KCN, by weight of the pig iron shows concentrations of cyanide vapor in hearth gasesrunning from 2 to 9 pounds KCN per 1,000 cubic of 5 pounds KCN per 1,000 cubic feet of gas is equivalent to something over 20 per cent cyanide by weight of the pig iron in a furnace makin 500 tons a. day with 40,000 cubic feet of wind a minute. Apparently, 5 per cent of the gas carries more than the equivalent of all the potash going into the furnace. Such is the index of cyanide accumulation.

These observed indication of immense accumulations of cyanide have led to the hypothesis that the well known function of the blast furnace in gas production is associated with the chemical activity of the blast nitrogen. In fact, the furnace functions to deliver producer gas containing about half the calorific energy of the coke. It also functions to fix as cyanide vapor a substantial percentage of the blast nitrogen. The two facts appear to be associated. A concentration of cyanide vapor in the products of combustion formed at the tuyeres amountin to 5 lbs. KCN per 1,000 cubic feet indicates a fixation of over 2 per cent of the blast nitrogen, or 8 per cent by weight of the carbon gasified. Such an amount of nitrogen fixed in the form of cyanide vapor is suflicient to account for some 25 per cent or more ofthe hearth heat." Since, as has become well recognized, the ore burden is limited by a lack of heat available to the hearth or smelting zone of the furnace, it is now evident that the vaporization of accumulated cyanide is a weighty factor in the furnace economy. As a matter of simple fact the blast furnace functions as a nitrogen-fixing gas producer.

In the present invention it is an object to control and limit the accumulation of alkali cyanides in the blast furnace making pig iron and thereby to improve the smeltin efiiciency. It is an object not only to recover cyanide as a valuable by-product in iron smeltin but also to increase the production of pig iron by the simple procedure of increasing the burden, that is, the ratio of ore to coke. Thus, the object becomes one of controlling the nitrogen-fixing function in order to make the furnace function more efliciently as an iron smelter and less so as a gas producer.

This object is accomplished by providing the furnace with one or more throttled outlets for cyanide vapor carried in hot gas through wide openings in the furnace wall at a level where the cyanide concentration in the gas is great enough to permit extraction of large proportions of the cyanide input of the furnace in relatively small volumes of gas. This throttled outlet of wide cross sectional area is connected through a wide feet of gas (atmospheric conditions). An average conduit running upwardly, then horizontally to a narrow nozzle set in a horizontal plane and thus delivering the gas vertically downward through the nozzle into a cooling chamber where the cyanide is condensed and collected. Thus the invention provides both means and method of controlling the accumulation of cyanide by extraction thereof and of improving the smelting economy by adding burden.

In the accompanying drawing are shown diagrammatically means within the invention for controlling cyanide accumulation and for carrying on the described method.

In this showing the figure represents a throttled cyanide outlet for withdrawing gases through an opening in the wall of a blast furnace just above the bosh. In the figure a blast furnace A of usual construction with air bustle B is provided with a usual number of tuyeres, one of which is shown at T. Usual coolers C are shown in the bosh wall.

In the wall of the shaft S above the bosh is formed an opening running horizontally through the wall. This opening is lined by firebrick F forming an arch extending into the furnace with an extension E supported from the wall S. Outside the wall the arched lining runs into a sheet steel conduit D which enters the shaft opening 0 and is supported from the shaft shell by a metal hanger H. The conduit D is formed with a T piece K having a flanged end closed by a flange cover M which is detachable. The side arm of the conduit T is faced upwardly and connects with an elbow L serving to turn the conduit horizontally to connect with a fitting G which connects with the top of a chamber P. The fitting G forming the cover of chamber P, as shown, may be termed a throttling device. In itsbottom a refractory nozzle N is set in a horizontal plane so that the gas is directed vertically downward. The fitting G has its horizontal opening closed by a removable flange W permitting access to the nozzle N. In the top of fitting G immediately above the nozzle 9. stuffing gland R carries a cleaning rod I which is adapted to clear the nozzle opening of obstructions. The steel conduit D comprising T K, elbow L and fitting G connected through gasketed flanges is lined throughout with refractory insulating brick and may serve as a swivel connection between the a The function of chamber P is to cool the gas entering through the throttling nozzle N and to collect the cyanide as it is condensed and separated from the gas, This chamber may be any of the known devices for condensing cyanide vapor carried in blast furnace gas. Advantageously chamber P may be provided as shown with cooling water pipes Q for quick cooling of the gas. It has a hopper bottom U closed by a bell valve, through which collected cyanide is removed.

In the lower part of chamber P connection is made through valve V with the gas main X for disposing of the cooled gas following the separation and collection of condensed cyanide. This valve cooperates with nozzle N in controlling. and limiting the gas flow through the furnace wall opening 0. The throttling effect of nozzle N is a function of the difference in gas pressure between that in conduit D and the pressure inside chamber P. The latter pressure is controlled by valve V so that the pressure drop through nozzle N may restrict the gas flow through wall opening 0 to a velocity which does not move the solids out of the furnace. The pressure within the furnace may be 12 to 18 pounds per square inch above atmospheric and the wide wall opening and conduit with constricted nozzle N serves to slow down the lineal velocity of gas flow and to prevent the flow of solids out of the furnace. The ratio of the respective cross sectional areas of opening 0 and the opening of nozzle N may be as high as 1,000 to 1, if desired. With a furnace pressure at the outlet level of 15 lbs. gauge, a 24 inch conduit throttled by a one inch nozzle opening works well with a back pressure of 3 pounds per square inch in chamber P, that is, witrl': a pressure drop of 12 pounds per square inc In operation, a single throttled outlet as described, serves to withdraw a limited volume of cyanide vapor laden gas from the furnace carrying however a substantial proportion of the potash which enters the furnace in the materials charged. An outlet designed to carry 250 cubic feet of gas per minute may, as I have found, extract more than a pound of cyanide a minute. This is a. recovery of more than 1400 pounds cyanide a day. Thus, in a furnace making 500 tons pig iron and having in ore, coke and limestone an input of potash and soda sufllcient to form cyanide equivalent to not more than 1 per cent of the pig iron, or 5 tons KCN a day, a single throttled outlet extracts 14 per cent of the alkali input in about one half of one per cent of the gas produced at the tuyeres. This has an appreciable effect in limiting the cyanide concentration and accumulation. The action of the furnace is improved. It becomes more regular.

To extract more cyanide a second cyanideoutlet is installed. Something over half of the total alkali input may be recovered as cyanide through four outlets, each throttled to 250 cubic feet of gas a minute, a total withdrawal of 1,000 cubic feet carrying initially 5 pounds cyanide as an average. Usually four outlets suffice to cut down the cyanide accumulation to a point where the concentration of cyanid vapor in the hearth gases is materially lessened. The heat taken out of the hearth is thus lessened, the combustion temperature rises and this permits a most sub- 'stantial increase of the ore burden with concomitant rise in the production of pig iron.

There is, of course, in the present blast furnace rather wide latitude for improvement in fuel economy. Usually the furnace functions as a gas producer to the extent of about half the fuel energy. Seldom is the specific smelting efficiency above 40 per cent. In fact, the total heat generated in air combustion is about double the quantity of heat absorbed in metal and slag and burning limestone. The effect of this lack of balance is to gasify with CO: 15 to 20 per cent coke carbon in addition to that burning with air. This is known as solution loss. The effect is largely responsible for the gas producing function. Consequently when the heat taken out of the hearth in cyanide vapor is controlled and limited by the extraction of cyanide as described, an increase up to 20 per cent in the burden ratio is entirely possible with a substantial increase in the rate of driving to burn coke now lost in solution. With this increased efficiency in the smelting work it remains still under per cent. It has been found advantageous to extract from 50 to per cent of the cyanide input through throttled gas outlets. This leaves in'thefurnace sufficient cyanide to aid in the reduction of metal at high temperatures. Increase of burden acts beneficially in removal of coke sulfur because of increase in the ratio of slag to coke. The throttling of the gas outlets to limit and control cyanide accumulation in the furnace effects hot gas withdrawal without serious flow of stock materials out of the furnace. The outlet conduitD can be cleared however, when required, through removable flange M in the T piece K at times when the wind is off the furnace. Sometimes it is advantageous to fill this T with large irregular pieces of coke. The regulation of the gas flow is aided by valve V which establishes the back pressure against nozzle N.

I claim:

1. In a blast furnace for smelting iron ore with coke, one or more cyanide outlets adapted to control accumulation of alkali cyanide in the furnace, each of said outlets comprising a large horizontal opening running through the inwall above the bosh, a wide connected conduit fitted to said opening conveying gas in an upward fiow from said opening and having an elbow changing said upward flow to the horizontal, a connected fitting taking said horizontal flow and being provided with a narrow throttling nozzle constriction set in a horizontal plane and directing the flow of gas downward and a connected chamber receiving said downward flow through said nozzle.

2. In a blast furnace cyanide outlet according to claim 1, valve means connected with said receiving chamber for regulating the back pressure therein and for restricting the flow of gas through said throttling nozzle.

3. In a blast furnace, a wide horizontal opening in the furnace wall above the bosh communicating through a vertically upward conduit with a narrow nozzle set in a horizontal plane and delivering downwardly into a cooling chamber, the relative areas of the nozzle and the wall opening being such as to restrict the passage of solids out of the furnace.

4. A blast furnace provided with means for controlling the burden ratio of ore to coke comprising one or more cyanide vapor outlets of relatively wide area extending horizontally through the furnace wall above the tuyere level, connected heat insulated conduit means fitted to said outlets and directing the flow of vapor taken out-of the furnace first vertically upward and then horizontally, associated nozzle means turning the horizontal vapor flow downward and throttling the flow of vapor through said wall outlets to a low velocity, a cooling and condensing chamber receiving the downward vapor flow from said nozzle and connected valve means holding a substantial back pressure in said cooling chamber against the downward flow through said nozzle, the combination of throttled outlet means being adapted to limit and control the accumulation of potassium cyanide inside the blast furnace.

5. A method of removing cyanide vapor from a blast furnace which comprises withdrawing gas in a continuous flow from the furnace at a level where the temperature is high enough to keep cyanide in the vapor phase and directly through a wide horizontal opening in the furnacewall, turning said horizontal flow of gas upwardly after withdrawal, then turning the upward flow in a horizontal direction, finally directing the flow vertically downward by means of a throttling nozzle constriction into a condensing chamber against a back pressure of gas suilicient to maintain a low lineal velocity of gas flow through said furnace outlet and regulating said flow of gas by controlling said back pressure to a relatively low flow of gas carrying a relatively large amount of cyanide out of the furnace.

RICHARD FRANCHO I. 

